Electroencephalography (EEG) is a powerful, inexpensive, and underutilized neurodiagnostic tool. Recent technical advances have led to dense-array EEG, with 256-channel sensor nets that can be applied comfortably in 5 minutes, inexpensive, high-performance amplification and digitization systems, methods for exact sensor registration with MR images, and flexible pattern recognition and visualization software. If it were possible to accurately localize the neural sources of EEG activity to specific cortical networks, dense-array EEG could provide new insights in both clinical and research applications. These applications range from localizing seizure onset in neurosurgical planning for epilepsy to identifying the neural foundations of language comprehension in infancy. In Phase I, we showed it is feasible to use 5A impressed currents to measure the conductivity of head tissues, using a "bounded" electrical impedance tomography (bEIT) method in which the geometry of head tissues is specified with segmented MR images. Because the same EEG spectral range and electrodes are used for bEIT that measure the EEG, the bEIT procedure provides an efficient, low-cost specification of the electrical volume conduction through head tissues. This may lead to a major advance in EEG source localization. As evidence of this advance, the Phase I results showed that, in each of the human subjects examined with bEIT, the skull was five times more conductive than was assumed in classical source localization models. If confirmed in the Phase II studies, these results would provide a definitive resolution of the controversy over human skull conductivity in the current literature. The Phase II commercialization would lead to a fast, accurate, and inexpensive bEIT method integrated with each dense-array EEG recording, providing robust and reliable EEG source localization for infants, children, and adults. With dense-array bEIT measured as routinely as testing scalp electrode impedance, we can realize the promise of recent biophysical simulations suggesting that, with accurate correction for head-tissue conductivity, EEG provides spatial resolution of brain activity that is equal to or better than magnetoencephalography (MEG). PUBLIC HEALTH RELEVANCE: The conductivity scanning system created by this research project would provide accurate estimates of the conductivity of human head tissues that aids in the analysis of the brain's electrical activity with the electroencephalogram (EEG). Because data acquisition is fast, safe, and taken from the same scalp sensors that are used for the EEG, conductivity scanning would result in greatly improved information about the brain for both research and medical applications.